Method for testing and blending lubricants



United States Patent Oiiice 2,841,533 Patented July 1, 1958 1 2,841,533 METHOD FOR TESTING AND BLENDING LUBRICANTS John Bryant Matthews, Newton, Chester, and Eric iolni Clayfield and Thomas Vincent Whittam, Upton Heath,

Chester, England, assignors to Shell Development Company, New York, N. Y., a corporation of Delaware No Drawing. Application August 23, 1954 Serial No. 451,688 Claims priority, application Great Britain August 24, 1953 5 Claims. (Cl. 196-4) This invention relates to a method of determining the lubricating qualities of liquids, and more particularly pertains to a method of controlling the quality of lubricants by determining a certain property of the oil.

The standard physical properties of oils and oil compositions, such as viscosity, pour-point, flash-point and the like have proven to be unreliable as measures of their lubricating properties since in many cases such products, which apparently possess satisfactory physical requirements of the character described above, yet show markedly poor results in actual performance, such as in opera tion of engines, gears, or the like. Various apparatus and methods have been developed such as described in U. S. Patents 2,065,625; 2,174,021; and 2,228,671 in order to determine the lubricating quality of lubricating oils. However, even these techniques have proven to be unreliable since the criteria of what is a good or bad oil, as determined by these methods, is based on arbitrary standards and there is no actual correlation between these standards and the behavior of the lubricant in actual operation.

It has now been discovered that the quality of a lubri mining its spreading pressure on a surface of the same.

type as that with which it comes in contact during its use, and if when necessary, adjusting one or more conditions of manufacture or blending to ensure that the spreading pressure of the lubricant is maintained between limits predetermined experimentally according to the use to which the lubricant is to be put. The process of the present invention is also applicable to cases where the lubricating oils undergo alteration in composition and properties during use by periodically removing a sample, determining the spreading pressure of the altered sample and by adjusting conditions of the process of manufacture or by blending to readjust the spreading pressure to its original predetermined limits. i

In order to describe the manner in which the method of the present invention may be performed, the control of the manufacture of a lubricating oil by means of the values of the specified spreading pressures of the blending components and of the lubricating oil being produced,

will be taken as an illustration. If it is desired to blend two or more mineral lubricating oils from different sources or refined by different methods to produce a finished lubricating oil suitable for use as a crankcase lubricant, a number of different blends are examined for their spreading pressures on a solid surface, for example steel, and for their performance in the crankcase. From these data it is possible to establish that the measured spreading pressure of the finished lubricating oil should lie between certain limits, say x and y. Blending is carried out, samples of the product are taken periodically, and the measured spreading pressures of said samples on steel are determined. If the measured spreading pressure of an oil sample at any time falls below the lower limit x, the conditions of blending are modified in order that an increased percentage of the blending component of higher measured spreading pressure is blendedinto the lubricating oil being produced, in order that the measured spreading pressures of further samples of the lubricating oil produced shall lie between the limits x and y. Similarly, if the measured spreading pressure of an oil sample at any time falls above the upper limit y, the percentage of the blending component with the higher measured spreading pressure is reduced. If the upper limit y is specified to be infinity, blending is conducted in order that the measured spreading pressure of the oil being produced is maintained above the value x. The procedure outlined above illustrates the manner in which the results of measured spreading pressure may be employed to control the manufacture of lubricating oils.

To evaluate the measured spreading pressures of oils on a solid surface, a drop of the oil in contact with the solid surface is prevented from spreading on the solid surface by the restraining film pressure exerted by a surrounding monomolecular film of a substantially waterinsoluble and substantially oil-insoluble substance, such as high molecular weight alcohols or acids or esters, e. g., C to C aliphatic alcohols or acids exemplified by dodecanol, tetradecanol, hexadecanol, or the corresponding aliphatic acids or esters such as ethyl stearate, ethyl oleate, butyl ricinoleate, etc. The reproducibility of measurement of the spreading pressure using diiferent materials such as dodecanol, tetra-decan-Z-ol, hexadecanol or octadecan-Z-ol and similar solids such as steel is in the order of.0.4 dynes per centimeter. This confining film is spread on the surface of a thin layer of water above that part of the solid surface not on contact with the oil drop, so that the pressure exerted by the confining film can be controlled and measured by means of a film-balance. The restraining film pressure is then reduced until spreading of the oil on the solid surface commences, causing the water layer to recede from that surface. The measured film pressure at this balance-point is then just equal to the spreading pressure of the oil on the solid surface in this system. The measured film pressure at this point is not numerically equal to the true spreading pressure of the oil on the solid surface but is a relative measure of this property, being directly proportional to the true spreading pressure minus a constant. This measured :film pressure is, however, the more convenient value for adoption in refinery and blending practice.

Measurements of the spreading pressures of oils on solid surfaces, for example, steel may be carried out as follows: The steel consists of cylindrical plates of 4 centimeters to 5 centimeters in diameter and 1 centimeter in height having the upper surfaces ground flat and polished to a fine mirror-like finish. During the tests, the plate is supported on an adjustable stainless steel platform and is set in an accurately levelled position in the trough of a film balance. This supporting platform remains in a fixed position under the water surface throughout a series of measurements. Tests may be conducted as follows:

(1) The steel plate is cleaned by means of methanol and a stream of benzene vapor and allowed to dry, in order to give a metal surface of a reproducible cleanliness.

(2) The clean plate is placed in its position on the adjustable platform in the trough of the film-balance,

the surface of the distilled water in the trough is swept clean, and the height and horizontal position of the upper surface of the plate are adjusted in order that a layer of water 0.050 centimeter in depth is formed over A travelling microscope is used point, is added to the water surface so that on compression of the monomolecular film thus formed, a sufficiently high film pressure, measured with the film-balance, is

attained. i

(4) A 0.02 milliliter drop of the oil sample is added to the film-covered water surface above the center of the steel plate. This immediately breaks through the insoluble monomolecular surface film and, confined by the pressure of the surrounding film, remains in lens-like form with its underside in contact with the steel surface.

(5) After one minute, the restraining pressure of the surrounding monomolecular film is slowly decreased by increasing the film area. This gradual reduction of film pressure which increases the free energy of the filmcovered water surface, results in a decrease in the oilwater interface until an equilibrium stage is reached beyond which further reduction of film pressure results in a receding of the water layer and spreading of the oil on the steel. The film pressure at this balance point is then measured.

The composition of the solid surface whereon measurements of the spreading pressure of a series of lubricating oils are carried out is not critical, since the same relative differences between the measured spreading pressures of various lubricating oil samples is observed when each solid surface of a wide range of solid surfaces of varying composition is employed. However, the said surface is preferably of metal, for example, ferrous metals, e. g., iron and steel or alloy metals. In refinery practice it is advantageous to employ a surface which does not readily corrode in use, for example stainless steel. Measurements are generally carried out at a temperature of C., but a variation of the temperature within :2 C. of this temperature does not measurably affect the spreading pressure value obtained.

In one form of the invention the spreading pressure used for controlling the conditions of the refining or blending of lubricating oils is not the spreading pressure of the oil actually produced in said refining or blending, but is the spreading pressure of a sample of the oil produced in which there has been artifically induced an alteration in composition simulating the changes in composition which occur in the oil during its intended use. The method of treating the sample of oil to induce such alterations in composition varies with the use to which the oil is to be put. Thus, a laboratory bench test has been devised which simulates the changes in composition of lubricating oils which occur when they are used as crankcase lubricants. This laboratory bench test, hereinafter called the beaker test, is based on investigations that have shown that the changes in the compositions of mineral lubricating oils during use in engine crankcases are due to the formation of polymerized hydrocarbon substances by oxidation and polymerization reactions. It is possible to chose conditions for the mild heat-treatment of a lubricating oil such that the oxidation and polymerization reactions which occur in the oil undergoing the test correspond fairly closely to the reactions occurring in the oil in the engine. By suitably modifying the conditions of the test, such as by varying the temperature of the oil, the time of heating and the area of the oil surface that is exposed to the atmosphere, it is possible to produce artifically a sample of oil that corresponds to a sample of oil obtained from any particular engine after a particular period of operation.

For example, the conditions necessary to obtain a correlation between an oil subjected to the beaker test and an oil examined by a test which simulates service in a Hercules engine are as follows. A sample of the lubricating oil is heated in air for 34 hours at 120 C. in a 100 milliliter fiat-bottomed Pyrex beaker. The quantity of oil in the beaker is such that there is a layer of oil 2 centimeters deep in the beaker, with an exposed area of 12.5 square centimeters.

The present invention is illustrated by theifollowing examples.

Example I A mixture of a Pennsylvanian lubricating oil and a Bright Stock in the proportions of 1:4 by weight respec- Measured spreading pressure on steel of blended oil in dynes per centimeter Percentage by weight of mixture of Pennsylvanian oil and Bright Stock in solvent-refined oil Lubricating oils of measured spreading pressure values exceeding 20 dynes per centimeter were found to give the most satisfactory results with respect to crankcase cleanliness when used as lubricants in a Hercules engine.

In a commercial blending of the aforesaid lubricating oils, the proportions of the oils were therefore adjusted so that the measured spreading pressure on steel of the lubricating oil produced was inexcess of 20 dynes per centimeter. This was controlled by periodically testing samples of the blended oil being produced for its measured spreading pressure on steel and adjusting the proportion of the component oils accordingly. In this way, the production of a finished lubricating oil unfit for use in the Hercules engine, due, for example, to unrecognizable changes in the properties of different batches of the component oils, was avoided.

Example II Serious lacquering of the cylinder-bores of diesel engines occurred sometimes When using, as the crankcase lubricant, certain batches of mineral lubricating oil produced from the same feedstock and by the same process as other batches which did not show this defect. The reason for the differences in performance between various batches could not be discovered.

The measured spreading pressures on steel surfaces of eight samples of the oil after use in a typical diesel engine were determined, and also the cylinder lacquer deposit and the cylinder bore ratings of the engine from which each sample was taken were examined visually. Also eight samples of the unused oil were subjected to the beaker test, carried out by heating an amount of oil such as forms a depth of 4 centimeters in a milliliter beaker, and has an undisturbed oil surface of 12.5 square centimeters, in air at C. for 80 hours. The measured spreading pressure of each of the resulting samples was then determined. The results which were obtained are tabulated hereinafter, and show a correlation between the measured spreading pressure on a steel surface of the used oil and of the oil subjected to the beaker test and the tendency of the oil to cause cylinder lacquering.

The cylinder-bore rating varies from the value 0 to 10, the cleaner the cylinder-bore the higher the figure.

Measured Measured spreading spreading pressure pressure Cylinder of oil at of oil at bore rating Cylinder lacquer 011 Sample end of end of at end of deposit group engine beaker engine test test in test in dynes per dynes per centimeter centimeter 23. 8 24. 4 10.0 Little Lacquer. 21. 1 19. 3 9.8 Do. 17. 3 16. 8 9. 2 D0. 12. 9 13.1 6. 8 Moderate Lacquer. 11.5 11. 0 6. 9 D0.

5. 9 7. 5 4. 4 Heavy Lacquer. 9. 1 8. 9 2. 1 Do. 5. 8 9. 2 2. 2 D0.

The lubricating oils giving the most satisfactory results with respect to the lacquering of diesel-engine cylinder-bores were the oils which possessed measured spreading pressure values exceeding 15.0 dynes per centimeter after having been subjected to the engine test or the abovedescribed beaker test. The conditions of manufacture of the lubricating oil intended for this purpose were therefore adjusted in order that the measured spreading pressures of samples of the lubricating oils produced that had been subjected to the above-described beaker test were in excess of 15.0 dynes per centimeter. In this way, production of batches of the oil having bad cylinder lacquering properties was avoided.

Example III A rafiinate having a viscosity of approximately 150 seconds Redwood I at 140 F. was obtained by subjecting a mixture of Lagunillas and Tia Juana crude oils to solvent extraction with liquid sulphur dioxide in an Edeleanu process, and a diesel engine lubricating oil was manufactured by subjecting this ratfinate to treatment with an adsorbent earth. It was known that lubricating oils, samples of which have been subjected to the beaker test carried out under the conditions specified in Example H and which samples then possess a measured spreading pressure exceeding dynes per centimeter, are of good performance with respect to diesel engine cleanliness.

Manufacture of the diesel engine lubricating oil was carried out by subjecting the said rafiinate to treatment with 4% by weight of an adsorbent earth, marketed under the name Filtrol, together with 0.1% by weight of lime. The temperature and time of contact were 60 C. and minutes respectively. A sample of the lubricating oil so produced was subjected to the beaker test under the conditions specified in Example II, and the measured spreading pressure of the resulting sample was found to be 14.4 dynes per centimeter.

The conditions of manufacture of the diesel engine lubricating oil were therefore changed. The said raflinate was then subjected to treatment with 4% by weight of an adsorbent earth marketed under the name M. R. C. The adsorbent earth was employed together with 0.1% by weight of lime, and the temperature and time of contact Were 60 C. and 30 minutes as before. A sample of the lubricating oil so produced was subjected to the beaker test under the conditions specified in Example II, and

the measured spreading pressure of the resulting sample was found to be 12.5' dynes per centimeter.

The conditions of manufacture of the diesel engine lubricating oil were therefore changed. The said raffinate was then subjected to treatment with 4% by weight of an adsorbent earth marketed under the name S. R. C. The adsorbent earth was employed together with 0.1% by weight of lime, and the temperature and time of contact were 60 C. and 30 minutes as before. A sample of the lubricating oil so produced was subjected to the beaker test under the conditions specified in Example II, and the measured spreading pressure of the resulting sample was found to be 16.4 dynes per centimeter. Since this diesel engine lubricating oil produced was of satisfactory quality, as assessed by the spreading pressure of a sample thereof which had been subjected to the beaker test, manufacture of such oil from this particular raflinate was continued using 5. R. C. earth and the conditions specified above, for so long as the measured spreading pressure of the product, after the aforesaid beaker test, remained above 15 dynes per centimeter. When it dropped below this value, the "earths were again changed until the earth giving a product of the required spreading pressurecharacteristics was found.

Example IV lubricating oil of good performance with respect to cleanliness in internal combustion engines.

It was known that lubricating oils, samples of which have been subjected to the beaker test carried out under the conditions specified in Example 11 and which samples then possess a measured spreading pressure exceeding 15 dynes per centimeter, are of good performance with respect to engine cleanliness, and moreover, that the value of the measured spreading pressure of such samples is preferably as high as possible.

Manufacture of the lubricating oil was carried out by subjecting the particular rallinate mentioned above to treatment at the temperature of 60 C. with 3% by weight of an activated adsorbent earth, marketed under the name Filtrol, together with 0.1% by weight of lime. A sample of the lubricating oil produced was subjected to the beaker test under the conditions specified in Example II, and the measured spreading pressure of the resulting sample was found to be 13.3 dynes per centi-.

meter.

The conditions of manufacture of the lubricating oil were therefore changed. The raffinate was: subjected to treatment at a temperature of 200 C. with the same proportion and composition of adsorbent earth and lime as had been employed previously. A sample of the lubricating oil so produced was subjected to the beaker test under the conditions specified in Example II, and the measured spreading pressure of the resulting sample was found to be 16.9 dynes per centimeter.

The conditions of manufacture of the lubricating oil were again changed with the object of producing a lubricating oil, a sample of which would possess an even higher measured spreading pressure after being subjected to the beaker test. The raffinate was subjected to treatment at a temperature of 180 C. with the same proportion and composition of adsorbent earth and lime as had been employed previously. A sample of the lubricating oil so produced was subjected to the beaker test under the conditions specified in Example ii, and the measured spreading pressure of the resulting sample was found to be 18.5 dynes per centimeter. Manufacture of lubricating oil from this raffinate was therefore continued by conducting the required treatment with the adsorbent earth at a temperature of 180 C. for so long as the measured spreading pressure of the product, after the aforesaid beaker test, remained above 15 dynes per centimeter. When it dropped below this value, the temperature was again changed until a temperature giving a product of the required spreading pressure characteristics was found.

Example V A lubricating oil which was intended for use in internal combustion engines was refined by subjecting a lubricating oil raffinate to treatment with adsorbent earth in an earth treater. It was known that lubricating oils, samout by passing the raflinate through the earth treater, and,-

when necessary, through a sulphuric acid treater situated upstream with respect to the earth treater, prior to being passed through the earth treater.

The process was started by passing the ratfinate through earth treater only and the value of the measured spreading pressure of the product, after the aforesaid beaker test, was 15.3 dynes per centimeter. After some days operation, it was found that, owing to changes in feedstock, the measured spreading pressure of the product, after the aforesaid beaker test had dropped to 11.5 dynes per centimeter. The raffinate was therefore directed through the sulphuric acid treater before going to the earth Heater, and the measured spreadin pressure of the resulting product, after the aforesaid beaker test, was found to be 16.3 dynes per centimeter. After some further days operation, it was found that the measured spreading pressure of the product, after the aforesaid beaker test, had risen to a much higher value. This indicated that the sulphuric acid treatment was no longer necessary. The rafiinate was therefore directed straight to the earth treater without any sulphuric acid treatment. This change in procedure was repeated as and when shown to be necessary by the measured spreading pressure of the product after the aforesaid beaker test.

Example VI Various gear oils of approximately the same viscosity were treated by means of the David Brown disc machine, in which discs of steel and bronze revolve with diiferent surface speeds in loaded peripheral contact. Determinations of the measured spreading pressure on steel were then carried out upon unused samples of the same gear oils.

The results of both series of tests were tabulated hereinafter.

From the above data it became clear that oils having a measured spreading pressure exceeding 18 dynes per centimeter 'vs the most s. 'acto-ry result with respect to gear lubrication. Accordingly, the conditions of manufacture of the gear oils were therefore adjusted in order that the measured spreading pressures of the gear oils produced were in excess of 18 dynes per centimeter.

The method of controlling the quality of lubricating fluids such as lubricating oils as shown above has a very Wide application and may be applied to all oils used for the lubrication of engines and other machinery, for example lathes. This method may be applied to all petroleum lubricating oils, for example those petroleum lubricating oils which are derived from asphaltic, naphthenic and paraffinic base crude oils. The method of this invention may be applied to mineral lubricating oils that are produced either as distillates or as residues, to the refining of lubricating oils by treatments such as solvent extractic-n, sulphuric acid treatment and/or clay treatment, to the manufacture of synthetic lubricating oils, for example polymerized cletins and alkylated aromatic compounds such as polytertiary butyl naphthalencs, and to the blending of mixtures of mineral lubricating oils with synthetic lubricating oils. The present invention may be applied to the manufacturing or blending of bright stocks, gear oils, spindle oils and penetrating oils. In particular, this invention is applicable to the blending of mineral lubricating oils derived from different sources or refined by different methods. -t is also applicable to the production of additive or compounded lubricating oils, i. e. lubricating oils to which dopes suchas organic compounds, organometallie compounds and inorganic compounds are added to confer special properties upon the oil such as extreme pressure or to inhibit oxidation, sludge or corrosion. Compounds of this type include sulfur, chlorine and/or phosphorus-containing organic compounds, e. g.,

quer and sludge resistant mineral lubricating oil com-- position for the lubrication of engine and movable machine parts which has a spreading pressure value such that the measured film pressure is at least 15 dynes per centimeter for a system of a horizontal steel surface immersed in water and superimposed by a film of a waterinsoluble and substantially oil-insoluble C C 'alkanol surrounding a drop of said oil which simultaneously con-L tacts said steel surface, the water and the alkanol, which consists essentially of blending a mixture of mineral lubricating oil fractions, one of which has a spreading. pressure value such that the measured film pressure thereof is less than 15 dynes per centimeter as defined hereinbefore, so that the final mineral lubricating oil composition for the lubrication of engine and movable machine parts has a spreading pressure value such that the measured film pressure is at least 15 dynes per centimeter as defined hereinbefore.

2. A method for producing a stable, as well as a lacquer and sludge resistant mineral lubricating oil composition for the lubrication of engine and movable machine parts which has a spreading pressure value such that the measured film pressure is at least 15 dynes per centimeter for a system of a horizontal steel surface immcrsed in water and superimposed by a film of a waterinsoluble and substantially oil-insoluble C C alkanol surrounding a drop of said oil which simultaneously contacts said steel surface, the water and the alkanol, which consists essentially of blending a mixture of mineral lubricating oil fractions, one of which has a spreading pressure value such that the measured film pressure thereof is less than and the other oil fraction is more than 15 dynes per centimeter, as defined hereinbefore, so that the final mineral lubricating oil composition for the lubrication of engine and movable machine parts has a spreading pressure value such that the measured film pressure is at least 15 dynes per centimeter as defined above.

3. In a method according to claim 2, wherein said mineral lubricating oil is a mineral lubricating oil for use in internal combustion engines having a Spreading pressure of at least 15 dynes per centimeter.

4. In a method according to claim 2, wherein the mineral lubricating oil is a gear oil having a spreading pressure of at least 18 dynes per centimeter.

5. In a method according to claim 2, wherein the mineral lubricating oil is a compounded mineral lubricating oil having a spreading pressure of at least 15 dynes per centimeter.

References Cited in the file of this patent UNITED STATES PATENTS McCluer May 3, 1938 Morgan et al Feb. 27, 1945 OTHER REFERENCES Bondi: Physical Chemistry of Lubricating Oils,

pages 105, 320 (1951), Reinhold Publishing Corp., New York, N. Y. 

2. A METHOD FOR PRODUCING A STABLE, AS WELL AS A LACQUER AND SLUDGE RESISTANT MINERAL LUBRICATING OIL COMPOSITION FOR THE LUBRICATION OF ENGINE AND MOVABLE MACHINE PARTS WHICH HAS A SPREADING PRESSURE VALUE SUCH THAT THE MEASURED FILM PRESSURE IS AT LEAST 15 DYNES PER CENTIMETER FOR A SYSTEM OF A HORIZONTAL STEEL SURFACE IMMERSED IN WATER AND SUPERIMPOSED BY A FILM OF A WATERINSOLUBLE AND SUBSTANTIALLY OIL-INSOLUBLE C12-C18 ALKANOL SURROUNDING A DROP OF SAID OIL WHICH SIMULTANEOUSLY CONTACTS SAID STEEL SURFACE, THE WATER AND THE ALKANOL, WHICH CONSISTS ESSENTIALLY OF BLENDING A MIXTURE OF MINERAL LUBRICATING OIL FRACTIONS, ONE OF WHICH HAS A SPREADING PRESSURE VALUE SUCH THAT THE MEASURED FILM PRESSURE THEREOF IS LESS THAN AND THE OTHER OIL FRACTION IS MORE THAN 15 DYNES PER CENTIMETER, AS DEFINED HEREINBEFORE, SO THAT THE FINAL MINERAL LUBRICATING OIL COMPOSITION FOR THE LUBRICATION OF ENGINE AND MOVABLE MACHINE PARTS HAS A SPREADING PRESSURE VALUE SUCH THAT THE MEASURED FILM PRESSURE IS AT LEAST 15 DYNES PER CENTIMETER AS DEFINED ABOVE. 